Kendal is one area which is on the north coast of Java Sea. The biggest fish auction place in Kendal Regency is Tawang Fish Auction (TPI Tawang). One of kind of demersal fish that caught in TPI Tawang is Croackers Fish. Biological aspect is needed to manage the resources of Croackers Fish. The porpose of this study is to found out the biological aspects of Croackers Fish Landed in Tawang Fish Auction Market. The research did in Juny 2016. The method used in this research is survey method. The sampling was taken by using Purposive sampling. From the research on 390 fish. the length size of Croackers Fish range from 10,5 cm – 20,9 cm. The growth of served was negative allometric with value of b 2,8859. The condition factor of 0,94 are flat fish. size of the first captured fish (L50%) was 16,4 cm. The Gonad Maturity Level of male Croackers Fish was dominated by TKG II, while for female of Croackers was dominate by TKG III. The lowest Gonad Maturity Index for male of Croackers Fish was 0,154% dan the hightest was 0,456, while foe female fish the lowest Gonad Maturity Index was 0,56% and the highest was 8,82%. For both male and female fish, first mature gonad was obtained 18 cm and 17,5 cm, it means that the female of Croackers Fish was mature faster than the male. The fecundity ranged from 15.500-44.148 item and variance of diameter value range from 0,05 mm – 0,45 mm. Key Word; Croackers (Johnius sp), Biological Aspects, Kendal Waters.